The present invention relates to wheelchair casters. More particularly, the present invention relates to a retention device and a flutter dampening device for a wheelchair caster.
The common wheelchair is typified by a seat structure mounted on a frame that is supported above the ground by a pair of drive wheels and a pair of caster wheels. The drive wheels typically have a large diameter and are mounted on either side of the frame while the caster wheels typically have a small diameter and are mounted on the frame forward of the drive wheels.
To facilitate steering of such wheelchairs, each caster wheel is retained in a structure of the frame that allows the caster wheels to pivot 360 degrees. The retaining structure usually includes several bearing elements that receive a caster wheel stem extending from a fork which, in turn, holds the caster wheel itself.
A problem often encountered with these known wheelchairs is that the steering function of each caster wheel is degraded due to the retention structure being susceptible to contamination. For example, many retention structures are unprotected (or insufficiently protected) from contaminants introduced into the bearing elements when a user remains in the wheelchair during showering. After repeated exposure to the contaminants, the bearing elements begin to prematurely wear and thus deteriorate the free pivoting movement of the caster wheels.
An example of one such hub structure can be found in the wheelchair disclosed in U.S. Pat. No. 4,887,826 wherein a caster wheel stem is received within hubs 114, 116 and is allowed to pivot by bushings 123. One can see that contaminants are easily introduced into the bushings 123 through the opening facing upward in hub part 114.
Another problem is encountered with these known wheelchairs when the user only has one hand available for making adjustments to the caster wheels. For example, when tightening of the roller elements is needed to remove clearance caused by extended use of the wheelchair, many known caster wheel retention device designs require more than one hand to effect appropriate adjustment. Consequently, the user may actually be precluded from making necessary adjustments or must, at the least, enlist the aid of a second individual.
A further known problem among the caster wheel designs of prior art wheelchairs is the problem of caster wheel flutter or shimmy. Such flutter or shimmy is a self-excited vibration which occurs above a critical speed of the wheelchair and can cause a drag from the effected wheel that is so high that the wheelchair may be forced to one side or may even be turned over.
Attempts have been made to alleviate flutter in caster wheels of a wheelchair as evidenced by the publication "A Caster Shimmy Damper Design" by Kauzlarich, et. al.
The device in the Kauzlarich, et. al. design incorporates a spring-washer shimmy damper which places a washer in frictional contact with an outer race of one of the bearings in the caster wheel retention device. The frictional contact is maintained by means of a spring such that the shimmy phenomena is substantially suppressed. However, the Kauzlarich, et. al. device is not adjustable. Hence, if it is determined that a greater spring force is needed to adequately suppress the shimmy or if extended use has degraded the ability of the spring to provide suitable suppression, disassembly of the Kauzlarich et. al. device is required in order to replace or adjust the spring.